1. Field of the Invention
The invention relates in general to elevator systems, and more specifically, to elevator systems which utilize chain compensation for the weight of the hoist roping.
2. Description of the Prior Art
Chain compensation for the weight of the hoist roping in a traction elevator system has distinct economic advantages over wire rope compensation. The major drawbacks of chain compensation are sway and noise, both of which increase in intensity with car speed. Thus, chain compensation has been limited to use on relatively slow speed elevator systems, but considerable effort has been directed toward reducing sway and noise in order to enable the use of chain compensation at higher and higher car speeds. For example, U.S. Pat. No. 3,768,596, which is assigned to the same assignee as the present application, teaches an arrangement for reducing chain noise. This arrangement extends the upper speed limit for chain compensated elevator systems to about 500 feet per minute. This patent discloses the use of resilient spacers formed of a material such as rubber, which are disposed about alternate links of the chain. The spacers are dimensioned to fully extend the links of the chain to maintain them in their extended position, which reduces noise in the natural loop of the chain formed below the elevator car and counterweight, and it also reduces the noise due to the chain striking components in the hoistway due to chain sway. U.S. Pat. No. 3,810,529, which is also assigned to the same assignee as the present application, teaches an arrangement which successfully extends chain compensation to still higher speed elevator systems, such as 700 feet per minute, which arrangement eliminates sway and reduces the noise level to a greater extent than the use of resilient spacers on the chain itself. In the arrangement of this patent, the compensating chain is firmly guided by a chain wheel or sheave which has a groove formed in its outer periphery by spaced elastomeric members. Alternate links of the chain extend edgewise into the circumferential grooves. The intervening links rest flatwise on the outer peripheries of the elastomeric members, outside the circumferential groove. This arrangement provides silencing and guiding functions without scraping, digging and twisting of the chain links.
While the arrangement of the latter patent substantially reduces chain noise and it eliminates sway, a certain amount of car vibration and/or airborne noise may occasionally be experienced with chain compensation, especially at the higher car speeds, such as 700 feet per minute. It has also been found that the magnitude of such vibration and noise varies substantially from installation to installation. Thus, it would be desirable to further reduce vibration and noise due to chain compensation, and to be able to reliably obtain such reductions under the widely varying conditions encountered in different elevator installations.